1. Field of the Invention
The present invention generally relates to an automatic transmission control apparatus. More specifically, the present invention relates to a technology of determining which one of a plurality of frictionally engaging elements in an automatic transmission is malfunctioning (e.g., mistakenly disengaged) so as to cause the automatic transmission to fail and present a neutral state.
2. Background Information
In a geared automatic transmission, each of the gear ratios is achieved by selectively engaging and releasing a plurality of clutches and brakes (each generically referred to as a “frictional engaging element”). In some automatic transmissions, a planetary gearing is included, such as the one described in Japanese Laid-Open Patent Publication No. 2000-240785. This Japanese publication also discloses forcing an automatic transmission, which has a turbine speed sensor to detect a speed of a rotation of a turbine shaft, to shift to a safe (non-malfunctioning) gear after determining that a portion of the automatic transmission has failed.
In addition, this Japanese Laid-Open Patent Publication No. 2000-240785 discloses calculating a real gear ratio from a detected turbine speed and a detected output speed and then determining that the automatic transmission fails when the real gear ratio continues to differ from an instructed gear ratio for a predetermined time. Next, it determines the portion which fails by comparing the real gear ratio to the instructed gear ratio upon determination that the automatic transmission fails. And, it possesses a map set beforehand depending on the current instructed gear ratio and the portion which fails, forcing the automatic transmission to shift to a predetermined gear.
In view of the above, it will be apparent to those skilled in the art from this disclosure that there exists a need for an improved automatic transmission control apparatus. This invention addresses this need in the art as well as other needs, which will become apparent to those skilled in the art from this disclosure.